1. Field of the Invention
This invention relates to an improved device containing an inactive form of an acetylenic compound, having at least two conjugated C.tbd.C groups, for measuring the integrated time-temperature history or integrated radiation-dosage history to which a perishable product has been exposed.
2. Brief Description of the Prior Art
Acetylenic compounds, containing at least two conjugated C.tbd.C groups, being cyclic or acyclic, symmetrical or unsymmetrical, diynes, triynes, tetraynes or hexaynes, and hereinafter referred to a diacetylenes, are an extremely useful class of compounds. They undergo 1,4-addition polymerization in the solid state, upon exposure to thermal annealing or actinic radiation, including ultraviolet and gamma radiation, thereby resulting in highly colored polymers. Utilization of this class of compounds has been described in U.S. Pat. No. 3,923,622 (Baughman and Yee, 1975) for use as cyclically bound ladder polymers; U.S. Pat. No. 3,999,946 (Patel, Preziosi and Baughman, 1976) for use as time-temperature history indicators; U.S. Pat. No. 4,164,458 (Patel, Aug. 14, 1979) for use as crosslinking agents; U.S. Pat. No. 4,125,534 (Yee, Nov. 14, 1978) for use as thermochromic indicating materials and in indicia-display devices; U.S. Pat. No. 4,125,534 (Nov. 14, 1978) as new carbazole-type photoconductors and non-linear optical materials; U.S. application Ser. No. 038,011 (Baughman et al., May 11, 1979), for use in gradient-type recording devices, and U.S. application Ser. No. 817,069 (Patel, July 19, 1977), now U.S. Pat. No. 4,189,399 (Feb. 19, 1980) as new co-crystallized compositions.
As described in U.S. Pat. No. 3,999,946 (Patel et. al., Dec. 28, 1976) and above-referenced U.S. Application Ser. No. 038,011, diacetylenes can be used in indicators wherein exposure of a diacetylene compound, deposited on a substrate, to thermal annealing or actinic radiation will initiate a 1,4-addition polymerization resulting in a color change. The color change produced at any given point in time represents an integrated-image temperature history of thermal annealing or integrated exposure to actinic radiation.
U.S. Pat. No. 3,999,946, (see the sentence bridging columns 7 and 8; column 6, lines 16-19; column 7, lines 50-51) generally describes the preparation of the indictors by coating crystals of an active diacetylene compound onto a substrate which is then responsive to thermal exposure or exposure to actinic radiation. However, the prepared indicators have the disadvantage that they must be stored at low temperatures and protected from actinic radiation prior to use. The step of protecting the formed indicators, at low temperature during storage and shipping to the point of use, greatly increases the cost of production and introduces an element of uncertainty as to the reliability of the final readings of the devices after use.
U.S. Pat. No. 3,999,946 also discloses at col. 6, lines 36-50 that the solvent chosen for application will affect the activity of the acetylenic compound. Two pending applications disclose methods for converting inactive forms of acetylenic compounds to active forms: U.S. patent application Ser. Nos. 854,933 (Patel and Yee, Nov. 25, 1977) and 911,565 (Patel, June 1, 1978), now U.S. Pat. No. 4,195,055 (Mar. 25, 1980)
What is needed is a device containing a form of diacetylene which can be stored at ambient temperatures during and after manufacture, shipped by standard procedures, and which can be applied to an article and activated by simple means just prior to use.
V. Enkelmann, Macromol. Chem. 179, 2811-2813 (1978) discloses that 2,4-hexadiyn-1,6-diol-bis-(p-chlorobenzenesulfonate) can be obtained in a metastable active form which apparently is isomorphous to the monomer structure of 2,4-hexadiyn-1,6-diol-bis(p-toluenesulfonate), which structure was investigated by V. Enkelmann et al. in Anger. Chem. 89, 432 (1977).
D. Bloor et al., in Proceedings of NATO Advanced Research Institute on Molecular Metals (Les Arcs, France, Sept. 10-16 (1978)) disclose that 2,4-hexadiyn-1,6-diol-bis-(p-chlorobenzenesulfonate) is unreactive in solid state polymerization.
J. J. Mayerle et al., in a report distributed by IBM Research Division describe their crystal structure determination of the inactive form of 2,4-hexadiyn-1,-6-diol-bis-(p-chlorobenzenesulfonate). However, the reference does not describe or suggest the use of the inactive forms of diacetylenes in forming an indicator for use as an integrated time-temperature history indicator.
It has been found that 2,4-hexadiyn-1,6-diol-bis-(p-chlorobenzenesulfonate) forms an active modification and exhibits a different X-ray diffraction pattern compared to the conventional inactive form. The inactive form is incapable of undergoing 1,4-addition polymerization upon exposure to gamma radiation at room temperature or thermal annealing below its melting point, whereas the new active form exhibits the desirable characteristics of a time-temperature indicator.
Furthermore, it has been found that the inactive form of 2,4-hexadiyn-1,6-diol-bis(p-chlorobenzenesulfonate) can be coated on a substrate and converted to an active form prior to use by solvent or melt recrystallization processes. Thus, problems associated in storing and shipping the indicator prior to use are eliminated.